The present invention relates to a photocatalytic composition based on an aerial binder and the use thereof for producing water-based paints, in particular for interior applications.
Photocatalysis is a natural phenomenon relating to certain substances, called photocatalysts, which, when irradiated with light having a suitable wavelength, are capable of catalyzing various chemical reactions. In particular, in the presence of light and air, on a surface containing a photocatalytic substance, oxidative processes are activated which lead to the transformation and/or decomposition of organic and inorganic polluting agents (microbes, nitrogen oxides, polycondensed aromatic products, sulfur dioxide, carbon monoxide, formaldehyde, acetaldehyde, methanol, ethanol, benzene, ethylbenzene, methylbenzene, nitrogen monoxide and dioxide). These polluting and/or toxic substances are transformed, through the photocatalysis process, into harmless substances which are englobed in the matrix of the product, such as sodium nitrate ((NaNO3), calcium sulfate (CaSO4), calcium nitrate (Ca(NO3)2) and calcium carbonate (CaCO3).
Photocatalytic processes can therefore be used for considerably reducing the pollutants present in the environment, such as those produced by exhaust gases of automobiles, by factories, household heating and other sources, and, at the same time, for eliminating dirt, mold and bacteria which degrade the inner surfaces of homes, schools, offices, hospitals and other structures.
Photocatalysts are generally metal compounds such as titanium dioxide, TiO2, the most active and widely used, zinc oxide, ZnO, and other oxides and sulfides (CeO2, ZrO2, SnO2, CdS, ZnS, etc.).
Numerous efforts have been made for developing compositions containing a photocatalyst to be used for coating building surfaces, which can be applied using means normally adopted in the building industry, which guarantee a remarkable and long-lasting photocatalytic effect, at the same time guaranteeing a satisfactory aesthetic effect, obviously in addition to non-excessive costs, so as to allow application on a wide scale.
According to the known art, the photocatalytic product is normally englobed in paint or varnish formulations, with a conventional substantially organic base. However, these formulations, being of an organic nature, undergo a transformation action and/or catalytic decomposition catalyzed by the photocatalyst, consequently the properties of the coating applied degrade with time, with detachment and chalking phenomena, in addition to causing a rapid decay of the original photocatalytic properties.
Compositions based on cement comprising a photocatalyst are also known in the art.
Patent application WO 2009/013337, for example, describes photocatalytic compositions comprising: a hydraulic binder; a polycarboxylic or acrylic superfluidizing agent; a cellulose ether having a viscosity ranging from 10,000 to 120,000 mPas·s; an adhesion agent; a calcareous, silicic or silico-calcareous filler; a photocatalyst. These compositions are said to have rheological properties that make them particularly suitable for use on large surfaces, without dripping or deformations.
Patent application WO 2013/018059 describes a photocatalytic powder paint to be used diluted in water, which comprises: Portland cement with the addition of photocatalytic titanium dioxide in the form of nanoparticles; a calcareous inert product having a maximum particle-size below 100 μm; cellulose having a viscosity lower than 1,000 mPa·s; a fluidizing agent; an anti-foam agent; a vinyl polymer; pigments. This composition also comprises one of the following additives: metakaolin, calcium formate, and diatomaceous earth.
The Applicant has faced the technical problem of developing a photocatalytic composition based on an aerial binder which can be used for producing water paints, i.e. wall coverings having an extremely low thickness, in particular for indoor applications, capable of:    a) guaranteeing a high photocatalytic effect, stable with time, also with relatively low quantities of photocatalyst, normally lower than 10% by weight;    b) allowing the preparation and use of water paint with conventional means, in particular by painting, with optimal results in terms of uniformity of the coating and resistance of the same to atmospheric agents;    c) using products free of toxic or harmful effects, without using heavy metals and organic solvents, in particular aromatic solvents, so as to obtain a product having a content of volatile organic compounds (VOC) lower than 0.35 g/l.    d) obtaining a product which is highly transpiring and highly basic, capable of being perfectly combined with oxidizing radicals and pollutants present in our homes.